1. Field of the Invention
This invention relates to hair-dyeing compositions containing substantive hair dyes and to certain novel 1,2,3,4-tetrahydronitroquinoxalines useful therein.
2. Statement of Related Art
In addition to oxidation dyes, which are formed by the oxidative coupling of one or more primary intermediate components with one another or with one or more coupler components, substantive hair dyes play a prominent part in the dyeing of hair. Substantive dyes have the advantage that they can be used without the addition of oxidizing agents. The substantive dyes used are predominantly compounds belonging to the group of nitrobenzene derivatives. They are used either on their own or in combination with other substantive dyes, such as anthraquinone dyes, indophenols, triphenylmethane dyes, cationic azo dyes, or with oxidation dyes.
Hair-dyeing compositions of the type in question normally contain such substantive hair dyes in a cosmetic carrier. The cosmetic carriers used for the substantive hair dyes and for the oxidation dye intermediates, if any, additionally present to obtain certain color tones include creams, emulsions, gels, shampoos, foam aerosols, or other compositions suitable for application to the hair.
Good hair-dyeing compositions have to form the required colors with sufficient intensity. They must be readily absorbed by human hair without excessively staining the scalp. The coloration produced with them must show high stability to light, heat, perspiration, shampoos, and the chemicals used in the permanent waving of hair. Finally, they should be safe to use from the toxicological and dermatological viewpoint.
In addition, substantive dyes are required to show high compatibility with other dyes, for example with oxidation dye intermediates and with the components normally used in oxidation hair-dyeing compositions because substantive dyes and oxidation dyes are often combined with one another for color tone modification. Accordingly, high stability to reducing agents and oxidizing agents is necessary.
Among the substantive nitrobenzene derivatives, the nitroanilines and derivatives thereof play an important part because some of these dyes produce intensive, light-stable hair colors. However, the known substantive nitroaniline dyes have disadvantages in that, on the one hand, they show only limited solubility in water, which leads to problems during formulation of the hair-dyeing compositions, and on the other hand are not sufficiently fast to washing, i.e., the dye finishes fade considerably after repeated washing of the hair. In addition, it is difficult when using substantive dyes to obtain certain fashionable tints, particularly red tints. Hitherto, 2-nitro-p-phenylenediamine and amino-substituted derivatives thereof have generally been used for this purpose. However, most of these compounds show inadequate solubility or dispersibility in water. This often leads to uneven hair colors. In addition, there is a danger, particularly with dyeing compositions containing high concentrations of dyes to obtain certain color tones, but also with compositions containing only sparingly solubilizing carrier components, of the colors obtained being weaker than expected because the dyes crystallize out and remain in the dye bath instead of being absorbed onto the hair.